This invention is directed in general to document platens for electrostatographic reproduction apparatus, and more particularly to a document platen having features which assist in the placement of a document on a platen so as to assure proper registration of the reproduction electrostatographically formed on a receiver sheet.
In typical electrostatographic reproduction apparatus for reproducing information from a document, the document to be reproduced is placed on a support platen and subjected to light from an illumination source to form an image thereof. A lens assembly focuses the light image on a uniformly charged photoconductive member to expose the member whereby the charge pattern is altered and a corresponding latent image charge pattern is formed on the member. Alternatively, the image may be converted to electrical signals for driving a laser or light element array to expose the uniformly charged photoconductive member, or electrostatically alter the charge pattern on a dielectric member.
Pigmented marking particles are brought into contact with the photoconductive (dielectric) member and attracted to the latent image charge pattern to develop such image on the member. The member is then brought into registered contact with a receiver member and an electrostatic field applied to transfer the marking particle developed image to the receiver sheet from the member. After transfer, the receiver sheet bearing the transferred image is transported away from the photoconductive member, and the image is fixed to the receiver sheet by heat and/or pressure to form a permanent reproduction thereon.
Assuming that all of the components of the reproduction apparatus are properly operatively related and functioning in the proper timed sequence, the orientation of the reproduced information of a document on a receiver sheet is dependent upon the location of the document on the document-supporting platen. However, proper placement of the document on the platen by a casual operator is not a trivial matter. The wide variety of electrostatographic reproduction apparatus available today have a number of different relative locations for placement of a document on the respective platens in order to achieve proper registration of the reproduction made thereby. Particularly, a document may be registered on the platen at any corner or edge, and the document may be placed on the platen with its major dimension lying from front to back or from side to side relative to the reproduction apparatus. In order to lessen operator confusion as to where to place the document on the platen, some reproduction apparatus employ indicia located adjacent to the platen. However, such indicia must be correctly located initially to assure document registration, and are subject to damage or removal.